1. Field of the Invention
The present invention relates to a gas laser oscillator that generates a laser beam by exciting laser gas introduced into an electrical discharge tube through an electric discharge.
2. Description of the Related Art
A gas laser oscillator (or a gas laser cavity) for, e.g., a carbon dioxide laser, provides a high power laser beam having good beam characteristics at high efficiency, and thus can be advantageously used for precise laser beam processing. Recently, a gas laser oscillator has been widely used in a laser processing machine capable of machining a workpiece into a complicated shape at high speed, while being combined with a numerical control unit for controlling the irradiation position of a generated beam on a workpiece.
FIGS. 7A and 7B schematically show the general configuration of a conventional gas laser oscillator (a configuration similar to the illustrated gas laser oscillator is described in Japanese Patent No. 3614450 (JP-B-3614450)). The illustrated gas laser oscillator is, e.g., a carbon dioxide gas laser oscillator and includes, as shown in FIG. 7A, two electrical discharge tubes 151, 152, into which laser gas is supplied, provided with electrodes (not shown) for causing an electric discharge in the supplied laser gas. The discharge tubes 151, 152 are mutually linked through a discharge tube linking holder 155 with their axes linearly aligned with each other.
An end plate 165 provided with an output mirror 161 is attached through a discharge tube holder 156 to the end of one discharge tube 151 opposite of the discharge tube linking holder 155. Similarly, an endplate 166 provided with a rear mirror 162 is attached through a discharge tube holder 157 to the end of another discharge tube 152 opposite of the discharge tube linking holder 155.
Thus, a Fabry-Perot type resonator, in which the output mirror 161 and the rear mirror 162 are disposed to face each other, is constituted. In order to dispose the output and rear mirrors 161, 162 so as to mutually face in high precision, i.e., to ensure good alignment of the optical axes thereof, the end plates 165, 166 are interconnected to each other through a support rod 170. The support rod 170 is made of an Invar alloy having a small coefficient of thermal expansion in order to prevent the optical axes of output and rear mirrors 161, 162 from being deviated from each other due to change in ambient air temperature or an increase in the internal temperature of the laser oscillator.
The discharge tube linking holder 155 mutually linking the discharge tubes 151, 152 is secured to the support rod 170 through a holder clamp 175 formed integrally with the holder 155 and forcibly cooled by, e.g., water cooling. Laser gas flows in a direction shown by an arrow in the drawing. The temperature of the discharge tube linking holder 155 rises due to flow of the laser gas heated by electric discharge, while the holder clamp 175 is forcibly cooled. Therefore, it is possible to prevent positional deviation of the discharge tube linking holder 155 relative to the support rod 170, and thus to eliminate an influence on the alignment of the optical axes of output and rear mirrors 161, 162 due to the positional deviation of discharge tube linking holder 155.
FIG. 7B shows a high power laser oscillator having the above basic configuration. In the illustrated high power laser oscillator, a plurality of discharge tube arrays 153A, 153B, 153C, each including a pair of electrical discharge tubes 151a, 152a, 151b, 152b, 151c, 152c, are arranged parallel to each other, the output mirror 161 and the rear mirror 162 are respectively disposed at the ends of discharge tube arrays 153A, 153C located at lateral ends of the parallel arrangement, and returning mirrors 163, 164 are disposed between the respective ends of discharge tube arrays 153A, 153B, 153C arranged in parallel. In this configuration, the optical axis of laser beam is turned back in multiple stages, and thereby all discharge tubes 151a, 152a, 151b, 152b, 151c, 152c are optically connected in series. The pair of electrical discharge tubes 151a, 152a, 151b, 152b, 151c, 152c of each discharge tube array 153A, 153B, 153C are mutually linked through the discharge tube linking holder 155 common to all discharge tube arrays 153A, 153B, 153C, and the discharge tube linking holder 155 is secured to the support rod 170 through the holder clamp 175.
In the above prior art, consideration is given so as to prevent the positional deviation of the discharge tube linking holder relative to the support rod due to the temperature rise of the gas laser oscillator associated with electric discharge, and thus to eliminate an influence on the alignment of the optical axes of the output and rear mirrors. However, especially in a high power laser oscillator including a plurality of discharge tube arrays, consideration is not sufficiently given to an influence on the optical axis alignment of the output and rear mirrors due to the thermal deformation of the discharge tube linking holder caused in association with electric discharge, or to the positional deviation of the discharge tube linking holder due to acceleration applied to the gas laser oscillator when the gas laser oscillator is physically displaced.